The nematic isotropic phase boundary, dilatometric properties and refractive indices of N-(p-hexyloxybenzylidene)-p-toluidine (HBT), N-(p-octyloxybenzylidene)-p-toludine (OBT) and their mixtures are reported. The density measurements of HBT, OBT and their mixtures indicate that all the nematic to isotropic phase transitions are first order transitions. The refractive indices data. along with the density data, are used to calculate the mean polarizabilities of the various HBT/OBT mixtures and to calculate the differences between the effective polarizabilities of the mixtures using both the Vuks and Neugebauer descriptions of the local field. Using the polarizability anisotropies calculated from the bond polarizability data and the Vuks determined effective polarizability differences, the order parameters of HBT. OBT and their mixture determined and are all seen to have approximately the same values.